The experiments proposed here are directed toward the investigation of mechanisms wich regulate RNA synthesis during differentiation. We wish to know how specific genetic units function in development and metabolism, what factors regulate transcription and the nature of the resulting gene products. We have chosen to study Drosophila melanogaster because of the extensive backround in genetics and cytology and because of the recent availability of permanent lins of cultured cells. We believe that studies such as we propose will help to give rise to an integrated view of chromosome function, incorporating, in the same sytem, genetic, biochemical, and cytological data in a way that cannot be approached in ay other eucarvotic system.